Solar Behaviour and the Atmosphere
If we are to understand the behaviour of the Earth’s atmosphere, then we must first understand the behaviour of the Sun. This is the source of all of the energy within the atmospheric structure. We must therefore ask just how does the behaviour of the Sun impact the Earth, what is the Sun doing now and what do we expect it to do in the future?
Many of the stars in the galaxy that we are able to observe, study and measure are highly variable, often pulsating and in many cases highly unstable, we are fortunate in that our own star, the Sun, is among those that have reasonably stable characteristics.
However, while observations indicate that the overall average Total Solar Irradiance (TSI), thermal energies, x-ray, and ultra-violet radiation – being the core constituents of solar energy – do remain fairly constant and reasonably stable, the sun occasionally and unpredictably gives off large scale explosive discharges, the most significant of which are Coronal Mass Ejections (CME’s). This phenomenon is defined as a burst of matter, gas, particles and energy from sun’s corona – the surface and atmosphere of the sun.
When this energy and material impacts the Earth’s magnetosphere, it compresses and distorts the magnetic fields surrounding the earth, induces large scale electric currents within the surface of the Earth and, as the material impacts, as the fields distort then re-establish and reconnect, terawatts of energy are injected into the Earth’s upper atmosphere.
While the energy injected is huge, it does not last long. Some thermal heating does occur, this is known and understood. Expansion occurs, density in the upper levels increases and this has been known to cause problems for low orbit satellites. This is a phenomenon referred to as ‘satellite drag’ and the temporary but measureable increase following a solar event is an example of the type of movement that we are concerned with. So what can we expect will happen to the atmosphere physically, at greater depths, at the levels and regions that may impact weather patterns?
If we think firstly in terms of movement of the Earth’s oceans, in effect the ‘water atmosphere’; interaction between the Moon and Earth causes variations in the gravitational field of the Earth, too small to be easily measured, however it is a variation that is enough to cause the oceans to swell and contract as the Moon circles the Earth. This change is very small when measured at the surface of the ocean, yet sufficient to cause large scale movement at critical points, at the coasts and rivers at the edges of the ocean where large scale tidal movements are readily observed.
We may now look at the movements of the atmosphere in a similar manner; however while the atmosphere is far lighter and less dense, it does have overall form, shape and weight and is subject to variations in density, expansion and contraction, under every outside influence. Injection therefore, of a huge amount of energy at all frequencies from the x-ray, the ultra violet, the infra-red, to the electromagnetic and magnetic/inductive, together with an intense bombardment of high energy particles will inevitably cause a physical reaction; an expansive surge similar to that measured in satellite drag. That expansion will cause increases in pressure, influencing the existing profile and gradient in the upper atmospheric structure, movement that will be observable most especially at the critical points within the profile where, potentially, large scale physical shifts may be expected. When that happens, surface weather patterns following the upper level profile are certain to be influenced. Cyclonic rotations at the surface level will tend to exacerbate the movement, dragging air masses more intensely, aggravating surface weather patterns.
But what of the future? We have said that TSI is, by and large, reasonably stable; or at least it has been over the decades during which we have had sufficient scientific knowledge and ability to measure it. There are however, indications that this may not always be the case. We know that ice ages and mini ice ages have occurred on earth in the past. We know that there have been periods when recorded solar activity has declined sharply; the periods known as the ‘Maunder Minimum’ of around 1645 to 1715 and the ‘Dalton Minimum’ of around 1790 to 1830, both of which coincided with abnormally low global temperatures and both of which may be part of a larger cyclical variation of which we have little understanding.
We know that at the present time, solar activity is declining rapidly, faster than at any time in the last 9000 years according to some scientific observers. The present solar cycle (cycle 24) peaked at around half of the level of recent cycles and the observed decline from the peak appears to be faster than would normally be expected, faster than predictions would have implied. Can we expect this decline to continue? We just do not have the knowledge to say, indeed predictions from just a few years ago suggested that solar activity would increase whilst in reality a sharp decrease has occurred.
On the basis of present observations the likelihood is, and the current predictions are, that this may indicate the commencement of a repeat of a Maunder-like minimum and is part of the larger, long time scale, natural cyclical variation in solar activity. It may be relevant to note at this point that, during periods of extended solar quiet, it is possible for sudden, abnormally large, sun spots and attendant CME events to occur. An event of this nature, known as the ‘Carrington Event’ occurred and was recorded in 1859 as the Dalton Minimum drew to a close. Should such an event impact todays technological society the results would be significant.